There was/is another way to power level crafters through the new leves, and that's what i did to get 5 crafting classes from 50 to 55 in less than 1h for 150k gil

Most of the new crafter leve turn ins are gear that the main/sub story quests gave as reward. And it's HQ!!

Not sure how other servers are, but i bought tons of stuff for like 4-5k HQ or even less in the first days of expansion.

I don't think this is an exploit. It was SE decision to give HQ gear as quest rewards and put them on crafting leves for hundreds of thousands of exp. And it was random players decision to sell it so cheap.

It's pretty much the same with the video here. There is no exploit.
You are getting low collectability from the highest level available ephemeral node. and this rewards you with lots of clusters and crystals.
High collectability would give you rare crafting materials that could possibly sell for more gil than 50 clusters are worth. Even if getting only 2 collectable things to aetherial desynth instead of 4.